There are, for example, image forming apparatuses that are provided with photosensitive members in correspondence with the colors yellow (Y), magenta (M), cyan (C) and black (Bk), and form a color image by transferring toner images of the respective colors to an intermediate transfer belt or the like so as to be overlaid on each other. In such an image forming apparatus, so-called color shift in which the relative positions of the different color toner images shift can occur. Color shift occurs due to factors such as write position shift in the main scanning direction, magnification shift in the main scanning direction, tilting or bending of scan lines in the main scanning direction, and write position shift in the sub-scanning direction.
Japanese Patent Laid-Open No. 2003-162117 discloses a configuration for forming a plurality of patch images for color shift detection on the intermediate transfer belt or the like, and calculating and correcting the amount of color shift, or in other words, the amount of position shift from a target position for forming the patch images, from the detected position of each patch image.
Furthermore, the density characteristics of images that are printed by an image forming apparatus vary due to the influence of factors such as change in the characteristics of components over time, variation in characteristics at the time of manufacture, and the use environment. Japanese Patent Laid-Open No. 2008-249714 discloses a configuration for adjusting density by forming a patch image for detecting density.
In Japanese Patent Laid-Open No. 2008-249714, first, light is irradiated by a light emitting element consisting of an infrared light emitting diode or the like onto a color toner image formed on an intermediate transfer body, and light that is specularly reflected at that time is received by a light receiving element for specularly reflected light, while light that is diffusely reflected is received by a light receiving element for diffusely reflected light. Here, the light receiving elements can be constituted by phototransistors, for example. The density of the color toner image is derived from the output of both light receiving elements.
At this time, the infrared light emitting diode and phototransistors are held by being enclosed in a package. Passageways are formed in the package for securing a light path for light irradiated by the light emitting element to travel to the object being irradiated, and a light path for light specularly reflected by the object being irradiated to travel to the light receiving elements. A passageway for securing a light path for light diffusely reflected by the object being irradiated to travel to the light receiving elements may also be formed in the package. A focusing mechanism member may also be provided for focusing on a detection location.
With conventionally known light amount detection sensors for patch images, it is, for instance, necessary to form large light passageways in the package, as described above, in order to separate specularly reflected light and diffusely reflected light, with this being a problem in that it leads to an increase in size of the light amount detection sensor. Even in the case where a focusing mechanism member is provided for focusing on a detection location, a similar problem of increased size arises. That is, there is demand for miniaturization of light amount detection sensors.
On the other hand, as mentioned above, it is envisioned that the sensor provided in the image forming apparatus will be used in correction control in different situations such as color shift control. That is, in addition to the above demand, there is demand for a highly convenient light amount detection sensor that is compatible with various patch images.